x+y=0.2,x+3y=1,求3x²+12xy+12y²的值

x+y=0.2,x+3y=1,求3x²+12xy+12y²的值
x+y=0.2,x+3y=1,求3x²+12xy+12y²的值

x+y=0.2,x+3y=1,求3x²+12xy+12y²的值
x+y=0.2,x+3y=1
两式相加
2x+4y=1.2
x+2y=0.6
3x²+12xy+12y²
=3（x^2+4xy+4y^2）
=3(x+2y)^2
=3×0.6×0.6
=1.08

2y=0.8
y=0.4
x=-0.2
3x²+12xy+12y²=3*0.04-12*0.2*0.4+12*0.16=0.12-0.96+1.92=1.08

3x²+12xy+12y²=3(x+2y)²
x+y=0.2，x+3y=1
所以x+2y=1/2(x+y+x+3y)=0.6
所以所求=1.08

x=-0.2，y=0.4
3x²+12xy+12y²=3（x²+4xy+4y²）=3（x+2y）²=3

配方啊 3x²+12xy+12y²=3(x+2y)²
x+y=0.2，x+3y=1
x+2y=1/2(x+y+x+3y)=0.6
答案1.08
先配方。再代入

两式相加得··2（x+2y)=1.2所以(x+2y)=0.6
所求式子=3（x+2y)^2=3*0.6^2=3*3.6=10.8